1. Field of the Invention
The present invention relates to a dynamic damper which is fitted onto a rotary shaft such as a drive shaft of a vehicle so as to damp vibrations of the rotary shaft.
2. Description of the Related Art
Conventionally, a dynamic damper of this kind includes a cylindrical mass metal element, and a cylindrical rubber elastic-body member which is attached to the mass metal element and fitted onto a rotary shaft whose vibrations are to be damped so as to elastically support the mass metal element on the rotary shaft. In the dynamic damper, in order to enhance adhesion between the mass metal element and the rubber elastic-body member, the mass metal element and the rubber elastic-body member are formed integrally by the steps of applying adhesive to the surface of the mass metal element and subjecting the resultant mass metal element to rubber vulcanization molding. In order to meet a conventionally existing demand for reduction in manufacturing cost, various studies have been conducted on a method for manufacturing the mass metal element and a process for manufacturing the dynamic damper. One of these studies concerns a nonadhesion-type dynamic damper, which is manufactured without use of adhesive.
For example, the dynamic damper (see FIG. 11) disclosed in Japanese Patent Application Laid-Open (kokai) No. 2000-240725 includes a cylindrical mass metal element 1, a cylindrical elastic-body attachment portion 3, and an elastic-body connection portion 4. The mass metal element 1 is covered with a rubber elastic-body covering layer 2. The elastic-body attachment portion 3 is formed from a rubber elastic body and coaxially disposed inside the mass metal element 1 while a predetermined radial distance is maintained therebetween. The elastic-body connection portion 4 is formed from a rubber elastic body and disposed between the mass metal element 1 and the elastic-body attachment portion 3 so as to connect the element 1 and the portion 3. A plurality of through-holes 1a are formed in the mass metal element 1 while being arranged circumferentially and located at the axially central position. The through-holes 1a are filled with the rubber elastic body, which has moved therein from the covering layer 2, thereby forming respective linkage portions 2a. The thus-formed linkage portions 2a can enhance retention of the mass metal element 1 effected by the elastic-body connection portion 4.
However, the above-described dynamic damper requires a step of drilling the through-holes in the mass metal element, which increases manufacturing cost. Also, when the mass metal element is to be manufactured through press bending, the through-holes may be arranged in an unbalanced condition, possibly impairing vibration-damping characteristics. Further, provision of the through-holes reduces the weight of the mass metal element, thereby narrowing the range of vibration-damping characteristics. In order to avoid this problem, the size of the mass metal element must be increased. Also, when the elastic-body attachment portion is fitted onto the rotary shaft, provision of the linkage portions formed in the respective through-holes produces a difference in contraction between the linkage portions and other portions which cover the mass metal element. As a result, a clearance may be formed between the mass metal element and the rubber elastic body, possibly impairing vibration-damping characteristics of the dynamic damper.
An object of the present invention is to solve the above-mentioned problems in the conventional dynamic damper and to provide a dynamic damper capable of retaining a mass metal element by means of an elastic-body member without use of adhesive and substantially increasing the mass of the mass metal element without increasing the size thereof.
To achieve the above object, according to a first aspect of the present invention, there is provided a dynamic damper comprising a cylindrical mass metal element, and a cylindrical elastic-body member disposed coaxially with respect to the mass metal element and fitted onto a rotary shaft whose vibrations are to be damped so as to elastically support the mass metal element on the rotary shaft. The elastic-body member is not bonded to the mass metal element. A plurality of protrusions are formed and arranged circumferentially on the surface of the mass metal element where the mass metal element is supported by the elastic-body member.
According to the first aspect, the mass metal element does not have radially extending through-holes formed therein and is not bonded to the elastic-body member, but instead a plurality of protrusions are formed and arranged circumferentially on the surface of the mass metal element where the mass metal element is supported by the elastic-body member. The protrusions are embedded in the elastic-body member, thereby reliably preventing circumferential movement of the mass metal element relative to the elastic-body member. Thus, the dynamic damper can implement enhanced retention of the mass metal element by means of the elastic-body member. As a result, use of adhesive is not required, thereby simplifying a dynamic damper manufacturing process and reducing manufacturing cost. Also, since the protrusions are embedded in the elastic-body member, the mass of the mass metal element can be substantially increased without need to increase the size thereof, thereby expanding the range of vibration-damping characteristics effected by the mass metal element.
According to a second aspect of the present invention, there is provided a dynamic damper comprising a cylindrical mass metal element; a cylindrical elastic-body member extending radially inward from the mass metal element toward a center axis of the mass metal element and fitted onto a rotary shaft whose vibrations are to be damped so as to elastically support the mass metal element on the rotary shaft; and an elastic-body covering portion covering the outer circumferential surface of the mass metal element. The elastic-body member and the elastic-body covering portion are not bonded to the mass metal element. A plurality of protrusions are formed and arranged circumferentially on the inner circumferential surface of the mass metal element.
According to the second aspect, the mass metal element does not have radially extending through-holes formed therein and is not bonded to the elastic-body member, but instead a plurality of protrusions are formed and arranged circumferentially on the inner circumferential surface of the mass metal element which comes into contact with the elastic-body member. The protrusions are embedded in the elastic-body member, thereby reliably preventing axial movement and circumferential movement of the mass metal element relative to the elastic-body member. Thus, the dynamic damper can implement enhanced retention of the mass metal element by means of the elastic-body member. As a result, use of adhesive is not required, thereby simplifying a dynamic damper manufacturing process and reducing manufacturing cost. Also, since the protrusions are embedded in the elastic-body member, the mass of the mass metal element can be substantially increased without need to increase the size thereof, thereby expanding the range of vibration-damping characteristics effected by the mass metal element. Further, since the protrusions are embedded in the elastic-body member, when the elastic-body member is fitted onto the rotary shaft, radial expansion of the elastic-body member imposes a compressive force on the mass metal element, thereby enhancing the retention of the mass metal element by the elastic-body member. Also, the elastic-body covering portion protects the mass metal element from smudging and corrosion.
According to a third aspect of the present invention, there is provided a dynamic damper comprising a cylindrical mass metal element; a pair of cylindrical elastic-body attachment portions disposed a predetermined distance outwardly away from corresponding axial opposite ends of the mass metal element while being coaxial with the mass metal element, the elastic-body attachment portions each having an inside diameter smaller than that of the mass metal element and being fitted onto a rotary shaft whose vibrations are to be damped so as to fixedly attach the dynamic damper on the rotary shaft; a pair of elastic-body connection portions adapted to connect the axial opposite ends of the mass metal element and the corresponding elastic-body attachment portions along the entire circumference; and elastic-body covering portions covering inner and outer circumferential surfaces of the mass metal element. The elastic-body connection portions and the elastic-body covering portions are not bonded to the mass metal element. A plurality of protrusions are formed and arranged circumferentially on the opposite end faces of the mass metal element.
According to the third aspect, the mass metal element does not have through-holes formed therein and is not bonded to the paired elastic-body connection portions, but instead a plurality of protrusions are formed and arranged circumferentially on the opposite end faces thereof, which are connected to the corresponding elastic-body connection portions. The protrusions are embedded in the elastic-body connection portions, thereby reliably preventing circumferential movement of the mass metal element relative to the elastic-body connection portions. Thus, the dynamic damper can implement enhanced retention of the mass metal element by means of the elastic-body member. As a result, use of adhesive is not required, thereby simplifying a dynamic damper manufacturing process and thus reducing manufacturing cost. Also, since the protrusions are embedded in the elastic-body connection portions, the mass of the mass metal element can be substantially increased without need to increase the size thereof, thereby expanding the range of vibration-damping characteristics effected by the mass metal element. Also, the elastic-body covering portions protect the mass metal element from smudging and corrosion.